JPH02279521A - Production of zirconia - Google Patents

Abstract

PURPOSE:To obtain high-purity ZrO2 excellent ij sintering property at low cost by melting zircon sand with CaO-contg. raw material by heating, then rapidly cooling, concentrating the Zr component from the product, leaching, precipitating, refining by a specified method, sintering and pulverizing. CONSTITUTION:Zircon sand and CaO-contg. material are mixed and molten by heating and then rapidly cooled to obtain a molten product which is soluble in acid. From this product, calcium silicate is selectively leached with dil. hydrochloric acid and then the zirconium component is leached with concd. hydrochloric acid, from which zirconium oxychloride is precipitated. The precipitated crystal is separated from the solution, dissolved in water, and allowed to react with sulfuric acid and (or) soluble sulfide to precipitate insoluble zirconium salt. This precipitate is separated, washed, and neutralized with alkali to produce zirconium hydroxide, which is dried, sintered and pulverized into zirconium powder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing zirconia, and more particularly, to a method for producing fine zirconia powder that does not contain hard aggregates and has good dispersibility. be.

[Prior art] Zirconium fine powder has conventionally been used as a raw material for sintered bodies such as ferroelectric materials, piezoelectric materials, catalyst carriers, solid electrolytes, heat-resistant materials, wear-resistant materials, and abrasive materials, as well as optical glass additives, thermal spray materials, and facial coating materials. It is used in a wide range of fields such as t1. Zirconia V/L powders used in these applications include those consisting of zirconia as a single component and those consisting of multiple components containing stabilizers such as magnesia, calcia, and ittria.

On the other hand, as research and development related to fine ceramics has become more active in recent years, the excellent properties of zirconia ceramics have attracted attention, and their use as high-performance electronic ceramic materials, high strength, high toughness ceramic materials, etc. is expanding. Demand for high-quality zirconia fine powder, which is the raw material for these products, is increasing.

Conventionally, the best method for producing high-purity zirconia for use in fine ceramics has been to use zirconium salts such as zirconium oxychloride and zirconium sulfate as starting materials, and to conduct a neutralization reaction or hydration from aqueous solutions of these salts. A method has been proposed in which a decomposition reaction generates a precipitate of zirconium hydroxide or hydrate, which is then dehydrated, dried, and calcined. A specific method involves adding an alkali such as aqueous ammonia to an aqueous solution of zirconium oxychloride to neutralize it to generate hydroxide, which is then filtered, washed,
A method of drying and then firing is used.

However, in this method, when neutralizing with alkali to produce a precipitate of zirconium hydroxide, Fe, AI, and T, which are present as impurities in zirconium oxychloride, are
Since zirconium i, Si, etc. are mixed as hydroxides along with the zirconium precipitation, purified raw materials must be used, and zirconium oxychloride from which impurities have been removed by recrystallization is usually used as the starting material. Was.

In addition, during the process of dehydrating and drying the zirconium hydroxide precipitate, the particles form a hard agglomerate that is strongly bonded to each other, and this shape is maintained even after firing. It was not possible to obtain a fine powder of zirconia, and the obtained fine powder of zirconia did not have satisfactory quality as a raw material for fine ceramics.

Therefore, in the process of dehydrating and drying the zirconium hydroxide precipitate, in order to prevent the formation of hard agglomerates, the zirconium hydroxide precipitate is dispersed in an organic solvent and distilled to remove water. v! Various manufacturing methods have been proposed, such as a method in which a solvent is separated and fired, a method in which a spray drying method is carried out, and a method in which a freeze drying method is carried out.

However, all of these methods have drawbacks such as requiring special equipment and using large amounts of organic solvents, resulting in high costs for industrial production methods.

In addition, among conventional methods, the so-called hydrolysis method, in which zirconium salts are hydrolyzed to produce hydroxides and hydrates, generally has a very slow hydrolysis reaction rate, so the decomposition reaction takes several tens of seconds under heating. It takes hours to several days, and the yield of decomposition products is low. Furthermore, since the zirconium concentration during decomposition is as low as 0.5 mol/e or less, a reaction tank with a large capacity compared to the production amount is required, and the reaction efficiency is low, making this method an industrially advantageous method. However, it had the disadvantage of high cost.

On the other hand, there is a method in which an alkoxide of zirconium, for example, an alkoxide such as zirconium isopropoxide, is used as a raw material and is heated in an organic solvent to hydrolyze it.
This method is disadvantageous as an industrial method for producing zirconia because the raw material price is high and the cost is high.

On the other hand, a method has recently been proposed in which zirconia is produced by pelletizing and firing a mixture of zircon sand and calcareous powder, dissolving the resulting clinker in relatively concentrated hydrochloric acid, and then neutralizing it (Tokuko Sho). 61-25658)
.

However, the purpose of this method is to economically produce zirconia in large quantities with a high recovery rate, and since the recovered zirconia is accompanied by impurities in the zircon sand ore, its separation is difficult. However, it has the disadvantage that it is not possible to obtain satisfactory results in terms of purity.

[Problems to be Solved by the Invention] The present invention overcomes the drawbacks of the conventional methods as described above, and produces particles with a particle size that can be used for the various uses mentioned above, including fine ceramics, through normal industrial operations. An industrially advantageous method in which fine powder of high-purity zirconia, which does not contain small, hard secondary aggregates, has good dispersibility, and has excellent sinterability, can be produced directly from impurity-containing zirconium raw material leachate. The purpose is to provide the following.

[Means and effects for solving the problem] The present inventors,
As a result of intensive research to solve the drawbacks of the conventional method, we mixed zircon sand with a calcium source such as lime, quenched it by electrolysis, and leached the zirconium-containing product with 11;i acid. zirconium oxychloride crystals are precipitated from the zirconium-containing leachate, a zirconium compound precipitate is generated from the solution containing the zirconium oxychloride crystals, and this is neutralized with ammonia, followed by dehydration, washing,
The present invention was based on the discovery that by drying and firing, a fine zirconia powder with high purity, small particle size, and good dispersibility that does not contain any hard aggregates and can be used as a raw material for fine ceramics can be obtained. completed.

That is, the present invention provides (a) a melt generation step in which a raw material mixture of zircon sand and a CaO-containing raw material is heated and melted, and then rapidly cooled to obtain an acid-soluble melted product; (b) the acid-soluble melted product and dilute hydrochloric acid; a step of concentrating the zirconium component in which the calcium silicate component is selectively eluted and separated by contacting with an aqueous solution; (c) a leaching step of contacting and dissolving the zirconium component with concentrated hydrochloric acid to recover a zirconium leachate; A crystallization separation step of precipitating zirconium oxychloride crystals from the leachate and separating and recovering the obtained crystals; (e) reacting an aqueous solution in which the crystals are dissolved with sulfuric acid and/or a soluble sulfate to form an insoluble zirconium salt; a zirconium recovery step in which a precipitate of the zirconium salt is produced; (a) a hydroxylation step in which the zirconium salt precipitate is separated and washed, and then the pulp slurry is neutralized with an alkali and recovered as zirconium hydroxide; and (g) the hydroxylation step The present invention relates to a method for producing zirconia characterized by comprising a zirconia forming step of drying, firing and pulverizing zirconium to obtain zirconia powder.

The present invention will be explained in detail below.

In the method for producing zirconia according to the present invention, first, in the melt generation step, a raw material mixture of zircon sand as a starting material and a CaO-containing raw material is heated and melted, and then rapidly cooled to obtain an acid-soluble molten product.

The raw material zircon sand used in the present invention can be a commercially available product as it is, but may be subjected to a pulverization operation if necessary.

In addition, quicklime, slaked lime, various types of calcium carbonate, etc. can be used as CaO-containing raw materials, and if necessary, coarsely crushed or
Alternatively, it can be used after being granulated.

In the present invention, the mixing ratio of zircon sand and CaO-containing raw material is important and must be determined taking into account the composition of the molten product. The raw materials are mixed and then melted and rapidly cooled. The reaction within the molten product in this case is considered to basically follow the reaction shown in the following formula (H).

2rSiO<+3CaO−+CaZr0ff+2CaO
・5iOt...(1) As shown in the above formula (1), the ratio of zircon sand and quicklime is 3 moles of CaO to 1 mole of ZrO, but in the actual reaction, impurities contained in the raw materials , Since there is some non-uniformity in raw material mixing, etc., CaO is added at a rate of 2.
The amount is preferably 5 moles or more, preferably 2.8 to 4 moles.

Next, the raw material mixture is heated and melted at 1500 to 2600°C, preferably 1700 to 2400°C, and then the molten product is rapidly cooled by pulverization or the like. This operation usually uses an arc furnace equipped with a Tatsuburo, from which the molten product flows out and is quenched by water pulverization by being blown with a high-pressure water stream.

By quenching by water pulverization, the zirconia component in the /8 fusion product can be made acid-soluble, and the zirconia component in the /8 melt can be made into an amorphous or acid-soluble calcium zirconate (CaZrOi).
can be obtained.

According to the research of the present inventors, zircon sand and quicklime are used to melt a mixture of 2.5 mol or more, for example 3 mol, of CaO per 21 mol of Z ro, and the molten product is pulverized. When rapidly cooled, X-ray diffraction analysis shows that CaZrO3
(JCPDS Card 35-790.1985) only the X-ray diffraction peak appears, and 2CaO.SiO2 is amorphous. On the other hand, if the molten product is gradually cooled, CaZr0. In the X-ray diffraction peak pond, 0
, 852r02 ・0 , 15CaO (JCP DS card 26-341.1976) or Z r O2
(JCP DS Card 17-923.1967) A similar X81 diffraction peak appears.

On the other hand, when less than 25 mol of CaO is mixed and melted with respect to 21 mol of Z r 021, and the molten product is pulverized and rapidly cooled, in addition to CaZr0t, 0.852r02·(1,
15caO5 or 7. rO2-like peaks appear. Furthermore, when 3 g of CaO2 mol is mixed with 1 mol of Zr0□ and 3 g is melted, the X-ray diffraction peak of CaZr01 no longer appears in the quenched product of the melted product, and 0.8
There are only peaks similar to 5ZrO□.0, 15CaO, or Z r O2.

Here, 0.85ZrOz・0.15CaO and Z r O
2 shows a nearly similar X-ray diffraction pattern,
In reality, it is estimated that a solid solution of 0 to 0.15 mol of CaO is produced with respect to Z r O2.

Furthermore, the present inventors investigated the solubility (elution) of the zirconia component in hydrochloric acid for various melted products. As a result, it was found that almost 100% of the zirconia component of the molten product in which only CaZrL was observed by X-ray diffraction analysis was eluted with hydrochloric acid of 2 mol/ml or more. In contrast, X-ray diffraction analysis revealed that in addition to CaZrOs, 0.
85ZrO,.0, 15CaO or ZrO2 was observed? 8 fused product is 0.85Zr02 +0.15
It was found that the elution rate of the zirconia component decreased as the peak intensity of CaO or Z r 02 increased. And there is no diffraction peak of CaZrL in the melted product, 0.85Zr02・O, l5CaO or Zr
In the case of only the diffraction peak of
% or less.

Based on the above findings, in order to melt a mixture of zircon sand and a CaO-containing raw material and make the zirconia component in the molten product acid-soluble, it is necessary to make the zirconia component in the molten product acid-soluble by X-ray diffraction analysis. It is important to create a composition in which only the crystalline phase can be obtained, and for that purpose, CaO is replaced by Z r O
0.85ZrO□・0.15
It is necessary to prevent the formation of CaO or ZrO2.

The acid-soluble molten product thus obtained is desirably pulverized to a powder having a particle size of 150 μl or less, preferably 100 μl or less.

If the particle size exceeds 150 μm, colloids of 5102 will aggregate on the particle surface during the next step of elution treatment with dilute hydrochloric acid, resulting in poor elution rate and resolution.

Next, in the step of concentrating the zirconium component, the calcium zirconate component and the calcium silicate component are selectively eluted and separated from the acid-soluble molten product slurry produced by contacting the acid-soluble molten product with a dilute aqueous hydrochloric acid solution. HC in slurry of acid-soluble molten product dispersed in dilute aqueous hydrochloric acid solution
By performing the elution under conditions where the l'a degree is less than 2 mol/2, as much calcium and silica as possible in the acid-soluble molten product can be eluted. The reaction formula is as shown in the following formula (II>).

CaZrO3+2CaO・5i02+4HCl-eCa
ZrOx+2CaCi'2+5i02+2820+
・+ (If) Specifically, use an amount 1.0 to 1.2 times the equivalent of H (l) in the reaction formula shown in the above formula (n), dilute with water to make 2 mol/ Elution is carried out in a hydrochloric acid aqueous solution having a concentration of less than p, and the calcium zirconate component of the elution residue is separated and recovered.

Next, in a zirconium leaching step, the calcium zirconate obtained in the leaching step is dissolved in contact with IR hydrochloric acid to recover a zirconium leaching solution. Calcium zirconate is immersed in a concentrated hydrochloric acid solution to remove H in the slurry.
Leaching is carried out under conditions where the Ce concentration is 2 mol/l or more, and the zirconium content is leached out.

Specifically, 1.0 to 1.2 times the equivalent of HCl in the reaction formula represented by the following formula ([[I)% formula%] is added to the calcium zirconate content of the elution residue from the above step. The leaching is carried out at a salt WIi concentration of 2 mol/l' or more.

Furthermore, in both the concentration step and the leaching step, there is no particular limitation on the slurry concentration in the eluate or leachate, as long as it satisfies a predetermined hydrochloric acid concentration.

Although there are no particular limitations on the elution or leaching in this case, the elution or leaching rate is generally faster when heated, and a temperature of 50 to 100'C is suitable.

In addition, when leaching the acid-soluble molten product with hydrochloric acid,
It is also possible to perform leaching in one step with 2 mol/l or more of hydrochloric acid, but in this case, calcium and silica are also leached together with zirconium into the leaching solution, and the silica that has been dissolved in the leaching solution is hydrated. Decomposition leads to insoluble silica precipitates, making subsequent solid-liquid separation extremely difficult.

Therefore, when leaching an acid-soluble molten product with hydrochloric acid, 1
As in the present invention, 2 mol/'! Industrially, two-step leaching is performed, in which the calcium and silica components in the molten product are leached as much as possible by leaching with less than 2 mol/l of hydrochloric acid, and then the leaching residue is dissolved in 2 mol/l or more of hydrochloric acid to leach out the zirconium content. There are 11 methods, which are one of the features of the present invention.

Next, in the zirconium oxychloride crystallization step, zirconium oxychloride (Zr01J2.8++20) crystals are precipitated and separated from the zirconium leachate obtained in the above leaching step. The method of evaporating and concentrating a soluble zirconium solution is generally used to precipitate zirconium oxychloride crystals, but this method is industrially disadvantageous because it requires special equipment and requires a large amount of energy. have.

In order to overcome the drawbacks of conventional methods such as evaporative concentration, the present invention
This method uses an operation that easily and efficiently precipitates high-purity zirconium oxychloride crystals by adding hydrochloric acid and/or calcium chloride to the zirconium eluate obtained as described above.

First, regarding the solubility of zirconium oxychloride in hydrochloric acid, the results shown in FIG. 1 are reported in the literature.

According to FIG. 1, it can be seen that the solubility of zirconium oxychloride draws a curve having a minimum value at a hydrochloric acid concentration of 8 to 9 mol/l. Therefore, according to this solubility curve, in order to maximize the recovery rate of zirconium, it is advantageous to crystallize zirconium oxychloride at a hydrochloric acid concentration of 8 to 9 mol/e. The zirconium concentration is 10 g/l or less as ZrO2.

On the other hand, according to results not certified by the present inventors, it has been found that when calcium chloride coexists with zirconium oxychloride, the concentration of hydrochloric acid at which the solubility of zirconium oxychloride becomes minimum shifts to the lower concentration side. It is also known that as the concentration of calcium chloride increases, the concentration of hydrochloric acid at which the solubility of zirconium oxychloride becomes minimum becomes lower. When trying to efficiently recover zirconium by precipitation, in a system where calcium chloride coexists in the zirconium oxychloride solution, the concentration of hydrochloric acid, where the solubility of zirconium oxychloride becomes minimal, shifts to the low concentration side, so it is necessary to add zirconium. The amount of hydrochloric acid required is small, and furthermore, since the liquid from which the crystals have been separated is small in volume and has a low acid concentration, there are advantages such as ease of treatment of the waste liquid.

Since the zirconium leachate according to the method of the present invention is obtained by eluting a zirconia concentrate mainly composed of calcium zirconate with hydrochloric acid, it inevitably contains calcium chloride. In precipitating crystals and efficiently recovering zirconium, the amount of hydrochloric acid used can be reduced as described above, and the method of the present invention can be said to be an excellent method for producing zirconium oxychloride.

Further, the relationship between the concentration of calcium chloride and the solubility of zirconium oxychloride is expressed by the curve shown in FIG. Second (
According to 2I, the saturation concentration of zirconium decreases as the concentration of calcium chloride increases, and as a solid phase, the saturation concentration of zirconium decreases with increasing concentration of calcium chloride.
In the solubility curve region shown in 21, Zr0Ce2・81
Only 1.0 exists in equilibrium.

Furthermore, as the concentration of hydrochloric acid increases, the solubility of zirconium decreases even at the same concentration of calcium chloride. As described above, it is clear that it is possible to add calcium chloride to the zirconium leachate obtained by the method of the present invention and recover zirconium as zirconium oxychloride. For example,
Add calcium chloride to zirconium leachate (CaCe232)
When added until 0 g/l, HCt! 2 mol/
In the case of Z ro 21, most of the zirconium is precipitated as calcium oxychloride crystals, and the dissolved zirconium is Z ro 21
0 g/1 (23°C) or less, and zirconia can be efficiently recovered. Furthermore, the concentration of the mother liquor from which the zirconium oxychloride crystals have been separated is relatively lower than that of hydrochloric acid, which is advantageous in terms of waste liquid disposal.

Various embodiments can be considered for the operation of adding hydrochloric acid and/or calcium chloride to the zirconium leachate to precipitate the zirconium oxychloride crystals as described above. There is a method of adding a predetermined amount of hydrochloric acid and/or calcium chloride to the solution, followed by slow cooling to precipitate zirconium oxychloride crystals.Next, the zirconium oxychloride crystals are separated from the mother liquor by a conventional method, and then Dissolve in a fixed amount of water to obtain an aqueous zirconium oxychloride solution. The amount of impurities in the zirconium oxychloride solution obtained in this way is reduced to about 1/l O in terms of Zr0a compared to the amount of impurities in the zirconium leaching solution, and Ti, Si, AI,
The concentration of impurities such as Fe is refined to 500 ppm or less based on 100% Zr02 as an oxide.

Next, in the method of the present invention, sulfuric acid and/or soluble sulfur F1 salt is added to the zirconium oxychloride solution to precipitate zirconium.

The amount of sulfuric acid conveniently added in the present invention is 0.2 to 0.6 mol per 1 mol of Zro in the zirconium oxychloride solution, preferably tL<0.3 to 0.4 mol. Desirably, when the amount added is less than 0.2 mol, no precipitate of insoluble zirconium is formed, and a thin milky white solution similar in appearance to silica sol remains;
．． If the amount exceeds 6 mol, even though the amount of sulfuric acid used increases, no commensurate effect can be expected; on the contrary, as the sulfuric acid concentration increases, the insoluble zirconium precipitate begins to be redissolved.

As described above, in the precipitation formation reaction in the zirconia production method of the present invention, the amount of H2SO added to ZrO□ is 0.
Although the amount is as small as 2 to 0.6 moles, it is possible to precipitate 95% or more of the zirconium in the zirconium leachate. Therefore, it is considered that the insoluble zirconium precipitate produced is not only obtained from the precipitation reaction of zirconium sulfate, but also something similar to the hydrolysis formation reaction of zirconium hydrate occurs simultaneously. in this case,
Although the effect of adding 6Q acid is not fully clear, it is consumed in the formation of zirconium sulfate precipitate, and zirconium exists in the state of polynuclear complex ions composed of several zirconium ions in the zirconium oxychloride solution. It is thought that the reaction between these polynuclear complex ions is catalytically promoted and the hydrolysis reaction is promoted.

The temperature of the reaction in which sulfuric acid is added to form a precipitate of insoluble zirconium from the zirconium oxychloride solution is not particularly limited, but since the reaction progresses faster in a heated state, it is usually between 50 and 100°C. is desirable.

The reaction time is determined in relation to the reaction temperature, but 1 to 4 hours is usually sufficient. If the time is less than 1 hour, the precipitation reaction has not progressed sufficiently, and 4
Even if the reaction is continued for a longer period of time, the precipitation rate will reach a plateau and will hardly contribute to improving the yield.
In the present invention, the reaction time may be 1 to 4 hours.
It has the characteristic that it completes in an extremely short time compared to normal hydrolysis reactions.

In addition, the zirconium concentration in the zirconium oxychloride solution to which sulfuric acid is added is desirably in the range of 3 to 15% by weight, preferably 5 to 10% by weight of ZrO2, and if it is less than 3% by weight, an insoluble precipitate will be formed. becomes extremely fine, making solid-liquid separation difficult, and when the separated precipitate is dried, there are problems such as the formation of hard silica gel-like aggregates, and if it exceeds 15% by weight, the precipitation reaction is inhibited. It is slow and produces very little precipitate.

Since the precipitated product of insoluble zirconium thus obtained is precipitated from a strongly acidic region, A1, Ti, Si,
Impurities such as Ca remain dissolved on the light side, resulting in extremely high purity.

As mentioned above, the method for precipitating zirconium in the method of the present invention is characterized in that it is carried out in the coexistence of sulfate ions in the solution, and soluble sulfate may be used instead of sulfuric acid, or both may be used simultaneously. There is no problem even if you do.

Next, in the hydration step, the slurry after separating and washing the insoluble zirconium salt precipitate produced in the recovery step is neutralized with an alkali and recovered as zirconium hydroxide.

Specifically, after solid-liquid separation of the insoluble zirconium precipitate obtained in the recovery step, the insoluble zirconium precipitate was repulped into water, and aqueous ammonia was added in an amount of 1.0 to 1.2 times the equivalent of the sulfuric acid used. In addition, after neutralization, zirconium hydroxide is recovered by solid-liquid separation.

Next, in the zirconia formation step, the zirconium hydroxide is dried, fired, and pulverized to obtain zirconia powder.

Drying can be carried out by any method such as spray drying, freeze drying, etc. in addition to the usual heat drying method.

The dried product obtained by the present invention is a powder with good dispersibility that does not contain any hard agglomerates and is easily loosened by finger pressure, and this property is retained even after the firing operation after drying.

Firing is usually carried out at a temperature of 200 to 1000°C for 30 minutes to several hours. The zirconia fine powder obtained in this way does not contain any tightly bound hard agglomerates, and is a bulky powder with good dispersibility. .

The zirconia fine powder obtained by the method of the present invention can be used as it is as a raw material for various sintered bodies, but it is also possible to improve the powder properties by pulverizing it. In this case, the crushing method is drying method,
Alternatively, a wet method may be used, and other known methods may be used as desired.

[Examples] The present invention will be specifically described below with reference to Examples, but the method of the present invention is not limited thereto.

Example 1 Zircon sand and quicklime were weighed and mixed uniformly so that the molar ratio of Zr0□ and CaO was 1=3, and then melted in an electric furnace. The heating melting temperature of the molten material at this time was 230
The melt was then quenched with a water stream at 0° C., dried and ground to obtain a molten product. As a result of analyzing this melted product, Zr0゜34.8%, Ca047.7%, 5i
It has a composition of 16.9% Oz, and the particle size is 150μ by sieving.
m or less. In addition, in X-ray diffraction analysis, CaZrOs
Only the diffraction peaks were identified.

Next, add 450 g of 7.51.35% water and hydrochloric acid to a 101 glass beaker, and while stirring, add 35 g of molten raw acid pulverized product.
0g was added and heated and held at 90°C for 2 hours.Then, this slurry was separated and the ZrO2 concentration in the P solution was measured and found to be 250 pp-, and the composition analysis in the molten product. Calculating from the results, the amount of Z r 02 leached was 1.8%.

The leaching residue obtained by Sawabetsu was washed into a beaker 11 with a small amount of water, and 450 g of 35% hydrochloric acid was added to bring the total amount to 500 g.
The slurry was then heated with stirring and held at 90° C. for 2 hours.Then, the slurry was separated and the filtrate cake was washed to obtain 800 ml of zirconium-containing leachate. The ZrO□ concentration in the leachate was measured and found to be 15.1%, and calculated from the composition analysis results in the molten product.
The leaching rate of Ox was 99.0%. Note that the leachate contains impurities such as Ca, Fe, AP, Ti, and Si, and as a result of quantitative analysis, Ca033.2%, ALOzo, 55%, and FexOs in terms of oxides relative to Zr02.
O507%, Na300, 01%, Sio20
．． 42%, Tio to, 34%.

Next, in a beaker 71, 850 g of 35% hydrochloric acid was added while heating the leachate to 75°C, and the mixture was heated to 75°C while stirring.
The mixture was slowly cooled to a temperature of 100.degree. C. to precipitate crystals of zirconium oxychloride. The obtained zirconium oxychloride crystals were separated from the mother liquor by Buchner filtration, and then dissolved in water to give zr0
A liquid 600+4 with a concentration of 11.4% was obtained. As a result of quantifying the impurities in the liquid in which this zirconium oxychloride crystal was dissolved, Ai'zO3 in terms of oxides with respect to Z r O2
0.05%, FezO, 0.01%, NazO 0.00
2%, S i O 70.04%, and TiOz 0.03%.

Next, put 325 g of this solution and 200 g of water in beaker 11.
Add 1 and heat while stirring, and when the temperature reaches 50℃,
9g of 98% sulfuric acid was added. Continue heating to 80℃
When , an insoluble precipitate of zirconium formed.

Furthermore, after holding at 80 to 90°C for 1 hour, the reaction was stopped. After solid-liquid separation, Z r O2 in the P solution was analyzed and found to be 1100 pp, and 97.3% of the dissolved zirconium was precipitated.

The insoluble precipitate is separated into solid and liquid, the r-filter cake is repulped in water, and further 28% ammonia water 139 is added to neutralize it, and the obtained zirconium hydroxide is separated into solid and liquid, washed and attached. Sulfate roots were removed.

A temporary cake of zirconium hydroxide is heated in an electric oven.
It was dried at 10°C for 8 hours. Dry powder is loose <11! It was a bulky item, and could be easily loosened with acupressure. This dried product was baked at 850°C for 2 hours. The obtained fired product does not contain any hard coagulum, and is monoclinic zirconia with good dispersibility.The crystal grain size determined by X-ray diffraction is approximately 210 g/cm, and the bulk density is 0.76 g/cm'. The tap density was 1.29 y/am', and the specific surface area was 23 m'/l.

In addition, the main impurity in ZrO2 is AZzO*20ppm
, FezOzl 7pp (Ti02140ppm, Ca
O was 10pp, and 5iO was 230pp.

Example 2 480 g of calcium chloride (40% CaCl'z solution) was added to 800 ml of a zirconium-containing leachate obtained in the same manner as in Example 1 to precipitate zirconium oxychloride crystals. The crystals were filtered through a Buchner to separate the zirconium oxychloride crystals, which were then dissolved in water and Z
600 ml of liquid with ro = ifi degree of 11.3% was obtained.

As a result of quantifying the impurities in the liquid in which this zirconium oxychloride crystal was dissolved, in terms of oxides with respect to ZrO2, AJIo, 0.06%, Fe2O, 0.02%, Na,
00.005%, 5iO20.04%, T io 20
．． 03 % Tea Atsuta.

Thereafter, a fired zirconia product was obtained in the same manner as in Example 1. The obtained fired product does not contain any hard agglomerates and is monoclinic zirconia with good dispersion control, and the crystal grain size determined by X11 diffraction is approximately 215 g, and the bulk density is 0.75 g.
/ am3, tap density 1.28g/c-1, specific surface 1
The main impurity in Z'02 was Al2O*2], ppm.

FetOzl 9pp (TiOz140ppm, CaO
13ppm, S 102230ppm.

Example 3 A solution in which zirconium oxychloride similar to Example 1 was dissolved in a 500@1' beaker (Z ro 211.4 weight 1%
) 325y and 177g of water and heat while stirring.
When the temperature reached 0°C, 9g of 98% sulfuric acid was added. When stirring was continued for an additional 5 minutes, an insoluble precipitate of zirconium began to form. After the formation of precipitate, 80 to 90
After holding at ℃ for 2 hours, the reaction was stopped. After solid-liquid separation, the concentration of ZrO in the r-liquid was analyzed and found to be 0.7.
0%, and 92.0% of the dissolved zirconium was precipitated.

The insoluble precipitate was separated into solid and liquid, and then repulped, neutralized, washed, dried and calcined in the same manner as in Example 1 to obtain zirconia powder.

The obtained powder does not contain any hard agglomerates and is monoclinic zirconia with good dispersibility, and the crystal particle size determined by X-ray diffraction is 212 particles, bulk density 0.77 g/cab'', and tap density 1. .30y/c+i3, specific surface area 22m''/g. Moreover, the main impurities in Z r O2 are AJ, 0.
12ppm, Fe2O* 2 81) pll, T
io t 1 2 0 ppm, Cao 201) i+
5iO22109p''.

Comparative Example 1 Zircon sand and quicklime were weighed so that the molar ratio of ZrO2 and CaO was 1=2, and melted in an electric furnace in the same manner as in Example 1. The temperature of the melt at this time was 1900°C.

Next, the melt was quenched by applying a water stream, and then dried and ground to obtain a melt product. As a result of analyzing this melted product, Z
ro 240, 1%, Ca036.8%, Si
It had a composition of O220, 1%. When the product was identified by X-ray diffraction analysis, there was no diffraction peak for Cdr02.
, 0.852rOt·0.15CaO or ZrOz diffraction peaks were only observed.

Next, this molten product (fine powder of 150 μm in diameter through a sieve) 202 was added to 5 mol/r hydrochloric acid 11, and Zr was leached out at 90 to 100° C. for 2 hours while stirring. When the slurry was separated from P and ZrO□ in the P solution was analyzed, 3
450 ppm, and the leaching rate of Z r O2 was 43.0% when calculated from the composition analysis results of the molten product. In this way, when the molar ratio of CaO to ZrO□ is 2, the melted product is 0.85ZrOz J, 15Ca
O or crystalline ZrO2 is obtained, and even when leached with hydrochloric acid, the ZrOx leaching rate is less than 5%, which is insufficient as an acid-soluble raw material for leaching zirconium.

Comparative PA2 Zirconium-containing leachate of Example 1 (ZrOa20.1
%) 184y and 300g of water were placed in a beaker of 11, heated while stirring, and when the temperature reached 50℃, 6g of 98% sulfuric acid was added.
was added. Further, stirring was continued for 2 hours at 80 to 90°C, but no precipitate of insoluble zirconium salt was formed, and a thin milky white solution remained. Thus, it has been found that when the molar ratio of H 2 S O 4 to ZrOz is less than 0.2 mol, no insoluble and separable zirconium precipitate is formed.

Comparative Example 3 Zirconium-containing leachate of Example 1 (ZrOz20.1
%H84y and water 3002 were placed in a beaker 11 and kept at 50°C while stirring.Next, aqueous ammonia was added dropwise thereto to neutralize.1. The dropping of aqueous ammonia was stopped with H3N2, and the mixture was kept at 50°C for 1 hour with stirring. After the slurry was separated from P, it was repulped with water, thoroughly washed, heated, and dried in an electric oven at 120° C. for 8 hours.

The obtained dried product was a silica gel-like aggregate that was extremely tightly bound, and even when ground using a mortar, a uniform fine powder could not be obtained, and the powder was rough to the touch.

In addition, the impurity content is At20z1320ppm, F
ezo 3470 ppll, Ca0251)l)II
, S io 2400ppm+, Ti0z2040pp
It was a cocoon.

[Effects of the Invention] As explained above, the method for producing zirconia of the present invention is capable of producing hard secondary aggregates with a small particle size by using normal industrial operations from zircon sand, which is a raw material containing impurities. It has the excellent effect of being able to provide industrially inexpensive high-purity zirconia with good dispersibility and excellent sinterability.

High-purity zirconia produced by the method of the present invention can be used for various purposes including as a raw material for fine ceramics, and is extremely useful.

[Brief explanation of drawings]

FIG. 1 is a graph showing the solubility of zirconium oxychloride in hydrochloric acid, and FIG. 2 is a graph showing the relationship between the solubility of zirconium oxychloride and the concentration of calcium chloride. Figure 1 λ xy) Hyzirconium (ZrOC1!z・8H20
) accuracy (23℃) CII]

Claims (9)

[Claims] 1. (a) A melt generation step of heating and melting a raw material mixture of zircon sand and a CaO-containing raw material and then rapidly cooling it to obtain an acid-soluble melted product; (b) bringing the acid-soluble melted product into contact with a dilute aqueous hydrochloric acid solution; (c) A leaching step in which the zirconium component is dissolved in contact with concentrated hydrochloric acid to recover a zirconium leachate; (d) Zirconium oxychloride is extracted from the zirconium leachate. (e) A zirconium step in which an aqueous solution containing the crystals is reacted with sulfuric acid and/or a soluble sulfate to form a precipitate of an insoluble zirconium salt. a recovery step, (f) a hydration step of neutralizing the repulp slurry after separating and washing the zirconium salt precipitate with an alkali and recovering it as zirconium hydroxide, and (g) drying and calcining the zirconium hydroxide. and a zirconia production step of pulverizing to obtain zirconia powder. 2. The method for producing zirconia according to claim 1, wherein the raw material mixture is a mixture in which the molar ratio CaO/ZrO_2 is in a range of 2.5 or more. 3. The acid-soluble molten product is amorphous or Ca
The method for producing zirconia according to claim 1, wherein only the ZrO_3 crystal phase is recognized. 4. The method for producing zirconia according to claim 1 or 3, wherein the acid-soluble molten product is a powder with a particle size of 150 μm or less. 5. 2. The method for producing zirconia according to claim 1, wherein the zirconium concentration step is carried out at a HCl concentration of less than 2 mol/l in the slurry. 6. 2. The method for producing zirconia according to claim 1, wherein the zirconium leaching step is carried out at a HCl concentration of 2 mol/l or more in the slurry. 7. 2. The method for producing zirconia according to claim 1, wherein the step of crystallizing and separating zirconium oxychloride is performed by adding hydrochloric acid and/or calcium chloride to the zirconium leachate. 8. In the zirconium recovery process, the molar ratio H_2SO_4/Z
The method for producing zirconia according to claim 1, wherein sulfuric acid is added so that rO_2 is in the range of 0.2 to 0.6 to insolubilize the zirconium content. 9. The method for producing zirconia according to claim 1, wherein the alkaline agent in the hydration step is ammonia.